As a sewing needle descends and penetrates material being sewn, the material sometimes can deflect the sewing needle sideways either laterally or longitudinally with respect to the stitching path. When this occurs, the loop thrown by the sewing needle beneath the material can be positioned out of alignment with the path of movement of a thread loop pick-up device. A thread loop pick-up device could be, for example, a shuttle hook, a rotary hook, or a thread looper. U.S. Pat. No. 2,577,430, entitled, "Needle Feed Sewing Machine" of A. C. Peterson et al, granted Dec. 4, 1951, discloses a sewing machine utilizing a thread looper. My prior U.S. Pat. No. 4,991,526, entitled, "Bedplate Insert and Presser Foot, Each Having a Guide Surface for Laterally Supporting a Sewing Machine Needle," granted Feb. 12, 1991, discloses a sewing machine utilizing an oscillating shuttle hook.
If the thread loop is out of alignment with the thread loop pick-up device, the sewing machine can miss a stitch. One cause of needle deflection is inconsistencies within the sewn material. The weave of the sewn material sometimes is not perfectly even or perfectly gridlike, and the fibers of the material can vary in thickness. Consequently, if the weave is at a bias, or at an angle going across the material, the needle naturally follows the angle of the weave, causing slight needle deflection.
In addition, certain types of non-woven material, such as leather, also have inconsistencies. The fibers that make up the animal hide are not entirely uniform. For example, depending on the part of the animal from which the leather comes, there are hard and soft spots, as well as scars, bites, and other inconsistencies, which may appear smooth, but which can cause needle deflection.
Other types of stiffer, more durable material, such as Kevlar, carbon fibers, plastics, and nylon webbings, for example, due to their rigidity and other factors, can cause needle deflection.
The foregoing causes of needle deflection are just some of the causes known to the inventor that can lead to missed stitches. These causes, as well as other causes, need to be controlled in order to minimize needle deflection and to ensure proper stitch formation.
In a sewing machine employing a needle feed mechanism, needle deflection during penetration of the material can be exacerbated when the material is advanced along the work surface of the sewing machine. In a needle feed mechanism, the sewing needle reciprocates back and forth along the stitching path, either alone or in conjunction with other components, such as a feed dog, to advance the material along the work surface of the sewing machine. When the needle reciprocates backward to advance the material, the natural resistance of the material tends to pull on the needle. As a result, the needle can be deflected out of alignment with the stitching path and, therefore, out of alignment with the path of movement of the thread loop pick-up device. When out of alignment, the thread loop thrown by the misaligned sewing needle can be missed by the thread loop pick-up device, which results in a missed stitch.
Accordingly, the present invention is directed toward a needle guide design for keeping the sewing needle aligned along the stitching path and with the thread loop pick-up device to reduce the occurrence of missed stitches.